Pilot Jimmy Boesen called the success a welcome relief after two sleepless nights: “The mission is 50% not done if we didn’t get it done. So it’s a good one.”

The loss of the remotely operated vehicle, capable of reaching a depth of 1,640 feet, had caused scientific data collection to stop while efforts focused on its retrieval.

The mission is on an unprecedented exploration of the Indian Ocean to document changes taking place beneath the waves that could affect billions of people in the surrounding region over the coming decades.

Mission director Oliver Steeds was relieved that the mission could now continue after the retrieval efforts had battled strong currents.

The mission has faced a number of mishaps: Bad weather forced a change of course. Fierce underwater currents have buffeted the submersibles, aborting dives.

The scientists on board the Ocean Zephyr now hope their luck has changed and that their mission to document the world’s least-explored ocean can kick into top gear.